Is the DC9-10 -> MD90-30 (assuming these the shortest and longest variants) a longer proportional length difference (and in absolute feet length terms), than the original Boeing 737 -> 737-900?Or is the longest 'stretch' maybe the 747 SP to the 747-800?

Original CRJ100/200 was 26.8 meters in length . The CRJ 1000 is 39.1 meters. That is a 46% increase in size. And do not forget that the original CRJ100/200 was a stretch from the Challenger jets, so the increase in size is even more.

Original CRJ100/200 was 26.8 meters in length . The CRJ 1000 is 39.1 meters. That is a 46% increase in size. And do not forget that the original CRJ100/200 was a stretch from the Challenger jets, so the increase in size is even more.

I think the biggest reason why aircraft with tail-mounted engines are better suited to longer stretches is because the wings are mounted further aft, which means there isn't as much distance between the main landing gear and the tail, reducing the possibility for a tail strike on rotation.

On aircraft with wing-mounted engines, the wings are further forward, so you have less room to rotate before chancing a tail strike.

It seems though that Boeing and Douglas always went up (except for the 720 and the 747SP) whereas Airbus goes both directions.

Depending on how you see it that's not always true. The 737-500 for example was a shortened 737-300. Of course the previous generation 737s (100 and 200) were shorter, but within it's generation the 737-500 was a shortening.

Not sure about the 737NG. I'm assuming the 737-800 was the base model here, so that makes the 737-600 and 700 shortened versions. Maybe longer than their previous generation counterparts, but shortened versions of their generations.

As mentioned, several of the Dougies and Maddogs, in addition to 735 and 736 as well as the A310, A318, A319, A342, and A345.

Another one that I don't believe has been said is the A332, also a shrink. Pretty sure the L1011-500 was a shrink too.

The A358 will be a shrink as well, if it's ever built... which I doubt.

One that's commonly assumed to be a shrink, but is NOT, is the 772LR.It came after the 773ER and incorporated most of its newer components, but it was actually built on the baseline frame, not a shrunken one.

Are the 717 frames different to the DC9? So not describable as a DC9 stretch?

It was a McDonnell Douglass design, so some aspects were certainly taken from the DC/MD frames. Once Boeing bought McDD they had two "new" aircraft they were producing. They chose the 737-600 (a shrink) over the 717. At the time, IMO they could have sold more 717's that 736's.

I think the biggest reason why aircraft with tail-mounted engines are better suited to longer stretches is because the wings are mounted further aft, which means there isn't as much distance between the main landing gear and the tail, reducing the possibility for a tail strike on rotation.

On aircraft with wing-mounted engines, the wings are further forward, so you have less room to rotate before chancing a tail strike.

The height of the MLG also plays an important role. The four wing mounted engine DC-8 -10/20/30/40/50/60 were stretched to the -60 (+24%) thanks to its height landing gear and s slight tilt forward. Same goes for the A340.

Not sure about the 737NG. I'm assuming the 737-800 was the base model here, so that makes the 737-600 and 700 shortened versions. Maybe longer than their previous generation counterparts, but shortened versions of their generations.

Are the 717 frames different to the DC9? So not describable as a DC9 stretch?

The Boeing 717 was supposed to be the MD-95.

As for another one---the CL600 series was stretched to the CRJ-100/200, CRJ-700, CRJ-900, and CRJ-1000. The CRJ-1000, at 128.4 feet, is a 60-foot stretch of the CL600 series. I consider this valid because it's the same type certificate. The DC-9 series has only a 49-foot stretch from DC-9-14 to the MD-90-30, the Boeing 737 50 feet from -100 to -MAX 10, and the A342-A346 is a 53-foot stretch.

As mentioned, several of the Dougies and Maddogs, in addition to 735 and 736 as well as the A310, A318, A319, A342, and A345.

The A342 and A343 were launched simultaneously. They were more of a family than a stretch/shortening.

I'm aware, but I'd still call it a shrink for two reasons:1) the A343 was to be the baseline moving forward, and the proposed A340-400, had it made it to market, would've been built off of that.2) the A342 suffered the fate of nearly all shrinks: similar platform & weights but less revenue space.

The CL600 to CRJ1000 huge stretch again says that rear engines may make for bigger stretches. Any clever explanation why this is so? Is it so?

One major limiting factor of stretching planes is scraping the tail during rotation or flare. Planes with aft-mounted engines don't stretch nearly as much behind the wing as they do in front of it ( heavy engines need more counterbalance), so they aren't impacted by tail strike quite so much. More specific to the CRJ, the 7/9 has a much taller main gear than the 1/2 did, giving it much more room to rotate.

Fun fact: the wheel base (distance from nose to mains) of a CRJ9 exceeds that of a B739.

CL600 is a corporate jet, so I don't think it is a fair comparison. Corporate jets are by their very nature quite short compared to their width.

They are all the same type certificate though. They are all CL-600s, from the first Challenger 600 to the CRJ-1000. It's astonishing that the cabin length was stretched from 8.6m to 23.6m, nearly triple the length!

So the 310 to 340-600 is a correct notion. Same class? They differ by 2 or 4 engines so in that aspect, they are different. However, same fuselage...same...

Facts are fun...

No, that's not correct. They got an entirely different wing design. The A330 / A340 got a much wider wingspan than the A300 / A310. Also the cockpit design is very different. Therefor the A300 / A310 is always considered a different family from the A330 / A340.

No, that's not correct. They got an entirely different wing design. The A330 / A340 got a much wider wingspan than the A300 / A310. Also the cockpit design is very different. Therefor the A300 / A310 is always considered a different family from the A330 / A340.

A340-300 and A340-600 have different wings. The 747-200, 747-400 and 747-8 also have different wings (and the -200 even a different cockpit), the 747SP has a different tail and different flaps. The 737-100 and 737NG have also different cockpits and different wing designs, the MAX adds a different tail design, the 707, 727 and 757 use actually only the fuselage, while nearly everything else is different. That means you can attach different wings, different tails, different cockpits, noses, gears and whatever. Still all of them use the same basic design for the fuselage. So yes, A310 to A340 is correct.